Question 1

To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a+b+c+d+e+strR and F- cells of genotype a- b- c- d- e- strS and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. The graph below shows the results of plating the cultures from each blender. What is the correct order of the genes on this chromosome? 
A) a b c d e
B) b e c a d
C) a c e b d
D) d a c e b
E) b e c a (d is unknown)

Accepted Answer

C

Question 2

A lab technician has four strains of bacteria. Although he forgot to label them, he knows that they include one F+ strain, one Hfr strain, one F' strain, and one F- strain. He observed the following results after plating these strains on different media. Which of the following plates can be used to identify the F- strain? $$\begin{array} { | l l l l l l | } 
\hline \text { strain } & \text { his } & g \text { gu } & \text { cys } & \text { leu } & \text { str } \
\mathrm { F } ^ { + } & + & + & + & - & + \
\mathrm { Hfr } & + & + & + & + & - \
\mathrm { F } ^ { \prime } & + & + & + & + & - \
\mathrm { F } & - & - & - & + & + \
\hline
\end{array}$$
A) minimal media with leucine and streptomycin
B) minimal media with histidine, glutamate, and cysteine
C) minimal media with histidine, glutamate, cysteine, and streptomycin
D) complete media
E) minimal media with streptomycin

Accepted Answer

C

Question 3

In five Hfr strains, each of which was used to build a time- of- entry map, the genes entered the recipient cells as follows: 
Strain 1: S L A C T F 
Strain 2: N P F T C A 
Strain 3: T F P N U Y 
Strain 4: S H Y U N P 
Strain 5: U N P F T C

Which of the following represents a correct compilation of these results
A) N P F T S L A C H U T
B) T C A L S P N U Y H
C) S L A C T F P N U Y H
D) S L A C T F P N H C U
E) U N P F T C A L S T F

Accepted Answer

The correct compilation of the results from the five Hfr strains, based on the order in which genes enter the recipient cells, is represented by option C: S L A C T F P N U Y H. This sequence is derived by aligning the overlapping gene sequences from each strain to form a continuous map.

Question 4

Which of the following is true of a bacterial strain that is his⁺ lac⁺ gal^- amp^R. A) It is unable to synthesize histidine. B) It is auxotrophic for histidine. C) It is unable to break down lactose. D) It will grow on ampicillin. E) It can use galactose as an energy source.

Accepted Answer

The bacterial strain is resistant to ampicillin (amp^R), so it will grow on ampicillin.

Question 5

An F' donor includes F DNA plus a segment of bacterial chromosome DNA. If conjugation is interrupted before the entire F' chromosome transfers, what could be the expected consequences?
A) a smaller F' plasmid than had been present in the donor
B) change of the recipient from F- to F+
C) formation of a recipient that is a stable partial diploid
D) integration of some but not all F' genes into the recipient's chromosome
E) failure of the F' strand to circularize in the recipient

Accepted Answer

The answer of An F' donor includes F DNA plus...

Question 6

Which of the following is false regarding plasmids?
A) They can have genes that promote their own transfer from one bacterium to another.
B) They contain essential genes for metabolism.
C) They can carry genes for antibiotic resistance.
D) They generally replicate autonomously.
E) They are small double stranded circular DNA molecules.

Accepted Answer

Plasmids are typically extrachromosomal DNA within bacteria that are not essential for basic metabolism but can provide additional functions such as antibiotic resistance. Essential genes for metabolism are usually found on the bacterial chromosome, not on plasmids.

Question 7

In generalized transduction, a phage introduces a segment of donor DNA into the recipient cell. This is followed by recombination of the donor fragment with the recipient chromosome. Which of the following must occur?
A) degradation of one of the two strands of phage genome
B) circularization of the donor fragment before recombination
C) a single crossover between the donor segment and the recipient chromosome
D) a pair (or even number) of crossovers between the donor segment and the recipient
E) replication of the donor segment before recombination

Accepted Answer

In generalized transduction, the donor DNA is packaged into a phage and transferred to a recipient cell, where it can recombine with the recipient's chromosome. For successful integration of the donor DNA into the recipient's chromosome, a pair (or even number) of crossovers between the donor segment and the recipient chromosome is necessary. This ensures that the donor DNA is properly aligned and integrated into the recipient's genome, maintaining the integrity and continuity of the genetic material. Single crossovers, circularization, replication of the donor segment before recombination, or degradation of phage genome strands are not requirements for this process.

Question 8

Which of the following is NOT a step involved in rolling circle replication during conjugation?
A) A protein complex known as the relaxosome cuts one strand of the F+ plasmid.
B) A double stranded plasmid is transferred to the F- cell through the conjugation pilus.
C) Rolling circle replication occurs in the donor.
D) Replication begins at the oriT after relaxosome binding.
E) Relaxase facilitates passage of the T strand into the recipient cell.

Accepted Answer

In rolling circle replication during conjugation, a single strand of the plasmid is transferred to the recipient cell, not a double-stranded plasmid. The transferred strand then serves as a template for synthesis in the recipient, while the remaining strand in the donor is also replicated.

Question 9

In the flow diagram shown below, which of the following is an inaccurate relationship between bacterial strains in the various F factor states? 
A) Link 1 represents transfer of an entire F plasmid.
B) Link 4 represents excision of the F plasmid plus some host DNA from the chromosome.
C) Link 3 represents precise excision of the F plasmid from the chromosome.
D) Link 2 represents integration of the F plasmid into the host chromosome.
E) All four links represent accurate relationships.

Accepted Answer

The answer of In the flow diagram shown below, which...

Question 10

To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a+b+c+d+e+strR and F- cells of genotype a- b- c- d- e- strS and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. The resulting cultures were then plated on medium containing streptomycin. Why? A) to eliminate non- conjugating Hfr cells B) to selectively eliminate cells that have taken in F⁺genes C) to eliminate non- conjugated F^-cells D) to eliminate all non- conjugated cells

Accepted Answer

The answer of To map genes of a bacterial strain,...

Question 11

When F+ conjugation occurs successfully, only one copy of the F plasmid single- stranded DNA is transferred. What else must minimally occur?
A) circularization plus replication of the new recipient DNA
B) circularization of the recipient's new DNA
C) rolling circle replication in the recipient cell
D) continuation of rolling circle replication in the donor cell and replication in the recipient cell
E) stopping the rolling circle replication after one copy length, circularization, and replication

Accepted Answer

During F+ conjugation, after the single-stranded DNA of the F plasmid is transferred to the recipient cell, it must stop rolling circle replication after one copy length, then circularize and replicate to form a double-stranded circular plasmid in the recipient cell. This ensures that both cells end up with a complete copy of the F plasmid.

Question 12

Which of the following allows the compilation of time- of- entry maps?
A) the recognition of phenotype interaction
B) the fact that gene entry can proceed in either direction
C) the use of many replicates of each experiment
D) the observation that Hfr genes recombine so efficiently
E) the use of appropriate controls repeatedly

Accepted Answer

Time-of-entry maps are created by observing the order and timing of gene transfer during bacterial conjugation, which can proceed in either direction from the origin of transfer in Hfr strains.

Question 13

Which of the following is NOT a step in transformation?
A) Donor cell DNA binds to a receptor site on the recipient cell.
B) DNA fragments pair with homologous regions of the recipient cell chromosome.
C) The donor cell lyses, releasing pieces of its chromosome into the environment.
D) DNA recombines with the recipient cell chromosome.
E) Both strands of the donor cell DNA are degraded.

Accepted Answer

Transformation involves the uptake of naked DNA from the environment by a recipient cell. The steps include the binding of donor DNA to the recipient cell, pairing with homologous regions, and recombination. The lysis of the donor cell to release DNA into the environment is also a part of the process. However, not both strands of the donor DNA are degraded; typically, one strand is degraded while the other is taken up by the recipient cell.

Question 14

To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a+b+c+d+e+strR and F- cells of genotype a- b- c- d- e- strS and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. What role does the blender play in the experiment?
A) shears the sex pili of conjugants
B) serves as a culture container only
C) acts as a mechanism to bring cells into contact
D) hastens conjugation events
E) speeds up molecular movement of DNA

Accepted Answer

The blender physically disrupts the mating pairs by shearing the sex pili, which are the structures that facilitate the connection between the Hfr and F- cells during bacterial conjugation. This interruption allows for the determination of the sequence in which genes are transferred.

Question 15

Jacob and colleagues developed a time- of- entry mapping technique. They used the genes for threonine and leucine synthesis (thr and leu), which are near the oriT site, as selected markers. Additionally, they used an E. coli F- strain P678 that has dysfunctional variants for all of the genes studied. They also used an HfrH strain that carried a functional allele for all genes studied. Which of the following statements is FALSE regarding the time- of- entry profile they acquired? 
A) The azi gene is closer to the thr and leu genes than the ton, lac, and gal genes.
B) The ton gene is found between the azi and lac genes.
C) Had the experiment continued, a time of entry map could be viewed for the entire E. coli chromosome.
D) The lac+ allele appears at about 16 or 17 minutes.
E) At 40 minutes, nearly 20% of exconjugants screened for the selected markers have the gal allele.

Accepted Answer

The answer of Jacob and colleagues developed a time- of-...

Question 16

Why does conjugation with an Hfr donor result in a much higher rate of gene transfer than conjugation with an F+ donor?
A) An F+ donor makes fewer pili.
B) The Hfr donor segment must undergo recombination in the recipient.
C) An F+ donor's T strand is slow to reach the pilus.
D) The Hfr donor transfers genes from the chromosome and not the plasmid.
E) The F+ donor segment must undergo recombination in the recipient.

Accepted Answer

The Hfr donor transfers genes directly from its chromosome into the recipient cell, allowing for a much higher rate of gene transfer compared to an F+ donor, which transfers genes from the F plasmid.

Question 17

Which of the following is incorrect about genetic analysis and mapping in bacteria and bacteriophages?
A) Generalized transduction uses lytic phage and specialized transduction uses a lysogenic phage.
B) Conjugation, transformation, and transduction all require recombination.
C) Conjugation requires cell- to- cell contact.
D) Conjugation, transformation, and transduction can all be used to map the order of genes on a bacterial chromosome.
E) Transformation requires a vector to carry donor DNA fragments to the recipient cell.

Accepted Answer

Transformation does not require a vector to carry donor DNA fragments to the recipient cell. Instead, it involves the uptake of free DNA fragments from the environment by a recipient cell.

Question 18

A competent bacterial strain with genes a, b, and c is transformed by a donor bacterial fragment. Cotransformation frequencies for each gene pair are as follows: $a$ and $b \quad 0.04 \%$
$a$ and $c \quad 0.02 \%$
$b$ and $c \quad 0.0064 \%$ Which conclusion can be definitively made from this data?
A) Cotransformation of b and c is so frequent, they must be one gene.
B) Gene b is closer to c than to a.
C) Gene a is closer to c than to b.
D) Gene order is a, b, then c.
E) Genes b and c are farthest apart.

Accepted Answer

Cotransformation frequency is inversely related to the distance between genes on a chromosome. The lower the frequency, the farther apart the genes are. Since $b$ and $c$ have the lowest cotransformation frequency (0.0064%), they are farthest apart.

Question 19

Which of the following statements about the T4 lytic life cycle is false?
A) Under the direction of phage genes, transcription and translation produce new phage components.
B) The phage DNA is injected into the host.
C) Progeny phage particles are released by lysis from host bacteria.
D) The phage DNA is integrated into the host chromosome.
E) The host DNA breaks down.

Accepted Answer

The T4 lytic life cycle involves the phage DNA replicating independently of the host DNA and does not integrate into the host chromosome. Integration into the host chromosome is characteristic of the lysogenic cycle, not the lytic cycle.

Question 20

Which of the following is an accurate statement regarding F factor states?
A) F+ and Hfr cells cannot convert exconjugants to a donor state.
B) F+ and F' cells cannot transfer donor genes to exconjugants.
C) An F+ cell can convert exconjugants to a donor state, as well as change their genotype.
D) An F' cell can convert exconjugants to a donor state, as well as change their genotype.
E) An Hfr cell can convert exconjugants to a donor state, as well as change their genotype.

Accepted Answer

The answer of Which of the following is an accurate...

Quiz 6: Genetic Analysis and Mapping in Bacteria and Bacteriophage

Which of the following is true of a bacterial strain that is his+ lac+ gal- ampR.

An F' donor includes F DNA plus a segment of bacterial chromosome DNA. If conjugation is interrupted before the entire F' chromosome transfers, what could be the expected consequences?

Which of the following is false regarding plasmids?

In generalized transduction, a phage introduces a segment of donor DNA into the recipient cell. This is followed by recombination of the donor fragment with the recipient chromosome. Which of the following must occur?

Which of the following is NOT a step involved in rolling circle replication during conjugation?

In the flow diagram shown below, which of the following is an inaccurate relationship between bacterial strains in the various F factor states?

When F+ conjugation occurs successfully, only one copy of the F plasmid single- stranded DNA is transferred. What else must minimally occur?

Which of the following allows the compilation of time- of- entry maps?

Which of the following is NOT a step in transformation?

Why does conjugation with an Hfr donor result in a much higher rate of gene transfer than conjugation with an F+ donor?

Which of the following is incorrect about genetic analysis and mapping in bacteria and bacteriophages?

Which of the following statements about the T4 lytic life cycle is false?

Which of the following is an accurate statement regarding F factor states?

Which of the following is true of a bacterial strain that is his⁺ lac⁺ gal^- amp^R.